| enigma(noun, trouble, show, difficulty, challenge) |
| conundrum(noun, trouble, show, difficulty, challenge) |
| mystery(noun, trouble, show, difficulty, challenge) |
| puzzle(noun, trouble, show, difficulty, challenge) |
| problem(noun, trouble, difficulty, challenge, question) |
| brain-teaser(noun, trouble, challenge, question, puzzle) |
| permeate(verb, fill, overrun, pierce, puncture) |
| closed book(noun, expression, idiom, trouble, challenge) |
| poser(noun, trouble, difficulty, challenge, question) |
| secret(noun, trouble, challenge, question, puzzle) |
| labyrinth(noun, secret, puzzle, complexity, maze) |
| screen(noun, verb, separate, arrange, examine) |
| puncture(verb, opening, sink, punch, stab) |
| pierce(verb, opening, sink, punch, penetrate) |
| question(noun, difficulty, secret, puzzle, obscurity) |
| sieve(noun, verb, separate, arrangement, opening) |
| perforate(verb, open, draw, use, opening) |
| puzzlement(noun, trouble, challenge, question, secret) |
| penetrate(verb, open, draw, use, sink) |
| bore(verb, open, draw, use, opening) |